Rechargeable zinc electrodes have application in secondary (rechargeable) cells and batteries that incorporate a zinc negative flat electrode (anode). Examples of such rechargeable cells and batteries in which the electrolyte is alkaline (aqueous KOH) are silver-zinc, zinc-air, nickel-zinc and manganese dioxide-zinc and other systems.
The usual practice to produce a zinc anode for zinc-air secondary batteries has been to prepare a paste containing the solid components of the anode and containing the electrolyte. US Patent Application 20060257744 teaches that an anode could be manufactured by mixing the zinc powder, an organic binding agent (which is used for shape stability), gelling agent and other solid components with an electrolyte to form a paste and pressing a current collector into the paste. U.S. Pat. No. 6,582,851 discloses the use of an encapsulation technique for surrounding the zinc/zinc oxide particles with a special material which induces the zinc to re-plate in the same mesh size as it was originally assembled. The paste of this material also contains organic powder material and liquid electrolyte.
Until now poor deep cycle lifetime has been observed in systems with these zinc anodes, typically below 200-300 cycles at depths of discharge (DOD) of above 50%. The zinc electrode is not highly stable on charge/discharge cycling in the alkaline electrolyte and the zinc active mass in the electrode tends to partially dissolve in the electrolyte and redistribute in a non-uniform manner. Another problem with such anodes is that the organic powder binder tends to coagulate as a film on the outside of the electrode. This reduces the effect of the binder in avoiding shape changes.
Two major failure modes have been encountered. In the first failure mode (dendrite failure) the cell shorts out on charge due to the uncontrolled growth of zinc dendrites between the zinc flat electrode and the opposing positive electrode, with the dendrites penetrating the separator between the electrodes. In the second failure mode (shape change failure) the zinc redistributes on cycling to gather on the lower portions of the electrode. This causes increased mechanical stress in the cell stack, a lower electrode active area, and a successively reduced capacity return (capacity fading) on cycling.